When you damaged your articular cartilage are you saying you had a bone bruise? I had that, but then after some months part of the cartilage broke off, it just never healed. I think you would really know if something like this happened. I don't think it is your graft loosening up though, I think you would know that too. You didn't mention any swelling. If you had a significant tear, I'm sure around the kneecap or in the back of the corner of the knee would swell a bit after activity. All I know is mine catches in that area all the time and I'm really not sure if it is my meniscus or my acl graft catching. I've always had a crickety crackedy knee, at least since my ACLR.